Computer optimized adaptive suspension system

ABSTRACT

A vehicle suspension system in which a computer controls damping and spring forces to optimize ride and handling characteristics under a wide range of driving conditions. A controllable shock absorber connected between the wheel and frame of the vehicle includes a hydraulic sensor which provides signals to the computer which are representative of the position of the piston within the shock absorber. The computer utilizes these position signals to control compression and rebound hydraulic pressure regulators by continuously computing, utilizing programmed algorithms, compression and rebound damping forces that will yield the desired ride and handling characteristics. An air spring may be connected with the shock absorber for compression and rebound along the same axis. Pressure sensors and air pressure inlet and outlet valves are connected to the computer for adjusting the pressure within the air spring to provide the desired spring rate.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. Ser. No. 523,279filed Aug. 15, 1983 now U.S. Pat. No. 4,468,050, and U.S. Ser. No.352,239 filed Feb. 25, 1982 now U.S. Pat. No. 4,468,739, the latterbeing a continuation-in-part of U.S. Ser. No. 322,200 filed Nov. 17,1981 (now abandoned).

FIELD OF THE INVENTION

The present invention relates to vehicle suspension systems, and moreparticularly to a vehicle suspension system in which a computer controlsdamping or spring forces or both to optimize ride and handlingcharacteristics under a wide range of driving conditions.

DISCUSSION OF THE PRIOR ART

Vehicle suspension systems have heretofore included shock absorbers,springs (coil, leaf, air or torsion bar), axle housings, torque arms,A-frames, anti-roll bars and stabilizers, among others. These componentshave been assembled in various combinations to produce the desired rideand handling characteristics of the vehicle. More accurately, becausemany compromises must be made, the ride and handling characteristics arechosen to be as close to desired as possible. In a typical suspensionsystem, changes in the spacing between axles and the body/chassis arecushioned by springs. Spring vibration is limited by dampers which areusually called shock absorbers.

In general terms a shock absorber is a velocity-sensitive hydraulicdamping device which uses hydraulic pressure to resist movement of thesuspension springs to limit and control the action of the springs.Piston velocity is a direct function of the speed of suspensionmovement. In any given shock absorber, a low piston velocity produceslow pressure and little control, while higher piston velocity generatesmore pressure and greater control. Wheel movements, that is, changes inthe relationship between axles (unsprung mass) and the chassis (sprungmass) are cushioned and controlled primarily by the suspension springs.The movement of the springs--spring vibration--is motion that must belimited, or damped by the shock absorbers.

It has been said that shock absorber design in one of the few facets ofautomotive engineering that remains more of an art than a science. Shockabsorbers typically dissipate energy stored in the springs by graduallyforcing oil through orifices and valves. The flow resistance encounteredby the oil results in compression and rebound damping forces whichcontrol the spring movement. The work done by the oil as it movesthrough the valves converts energy stored in the springs into heat whichis dissipated from the shock absorbers into the surrounding air. Theride can be made softer or stiffer by varying the fluid flow through thevalves and orifices.

The amount of force exerted by a spring is proportional to how far it isdeflected. The amount of force exerted by a hydraulic shock absorber isproportional to the velocity of the piston therein. Modern hydraulicshock absorbers include, for example, a six-stage valve system (threecompression stages and three rebound stages) to provide optimum controlat various piston velocities.

The goal in a conventional suspension system is to match the resistanceor control force of the shock absorbers to the forces generated by theircorresponding springs in a manner that will yield the desired ride andhandling characteristics. The control forces which conventional shockabsorbers exhibit during compression and rebound are determined by theirparticular bleed valves, blow-off valves, spring discs, blow-off springsor piston restrictions, etc. The damping curves (force versus pistonvelocity) of conventional shock absorbers are predetermined by theirconstruction and are not adjusted during vehicle travel. However, theresponses of such suspensions are fixed and their shock absorbers canrespond in a desired manner to only a limited range of conditions, witharguably optimum response available in an even more limited range ofconditions.

In the past various manual and automatic vehicle leveling systems havebeen devised for maintaining a predetermined height between the sprungmass of the vehicle (frame and body) and the unsprung mass (wheels,drive train, front axle and rear axle). Many of these systems pump airinto, or discharge air from, air springs to raise or lower the vehiclebody relative to its wheels. Exemplary vehicle leveling systems aredisclosed in U.S. Pat. Nos. 3,574,352, 3,584,893, 3,666,286, 3,830,138,3,873,123, 4,017,099, 4,054,295, 4,076,275, 4,084,830, 4,162,083,4,164,664, 4,105,216, 4,168,840 and 4,185,845. The principal object ofsuch vehicle leveling systems is to accommodate variations in vehicleload rather than to actively adjust shock absorbers and springs duringvehicle travel to improve ride and handling.

Other vehicle suspension systems have been developed for automaticallyaccommodating dynamic loading effects during vehicle travel. U.S. Pat.Nos. 2,967,062, 2,993,705 and 3,608,925 are directed to systems forcontrolling the roll of a vehicle, for example, during a turn. U.S. Pat.No. 3,995,883 discloses a vehicle suspension system in which awheel-to-body displacement transducer and an acceleration transducer onthe vehicle body produce signals which are utilized to vary the dampingforces in the system. U.S. Pat. No. 4,065,154 discloses a vehiclesuspension system in which signals from a plurality of wheel axlevelocity transducers are utilized in varying the damping forces. BritishPat. No. 1,522,795 discloses a vehicle suspension system in which anelectrically actuable spool valve controls the application of fluidpressure to a damping control valve.

Other actively controlled vehicle suspension systems are disclosed inU.S. Pat. Nos. 2,247,749, 2,973,969, 3,124,368, 3,321,210, 3,502,347 and4,215,403.

SUMMARY OF THE INVENTION

A primary object of the present invention is to provide an improvedvehicle suspension system which will automatically adjust itself duringvehicle travel to provide optimum ride and handling characteristicsunder a wide variety of driving conditions.

Another object of the present invention is to provide a computeroptimized adaptive suspension system which will automatically reduceroll, pitch and oscillation, provide improved wheel rebound control andabsorb large bumps optimally.

Still another object of this invention is to provide a vehiclesuspension system which will automatically maintain a selected butadjustable wheel-to-body height for varying loading conditions.

Yet another object of the invention is to provide a vehicle suspensionsystem capable of varying damping substantially independently of thevelocity of the axle relative to the vehicle body.

A concomitant and more general object of the invention is to reduceshock absorber design and operation to a predictable science.

In the illustrated embodiment, a combined shock absorber/air spring unitis connected between the wheel and frame of a vehicle. It should beunderstood that the shock absorber or air spring unit can each beseparated and either can be used alone with the other being ofconventional design. The shock absorber includes a hydraulic sensorwhich provides signals representative of the position of the pistonwithin the shock absorber and therefore of the position of the chassiswith respect to axles. The computer utilizes these signals to controlcompression and rebound hydraulic pressure regulators to producecompression and rebound damping forces that will yield the desired rideand handling characteristics. The air spring may be connected in seriesor in parallel (concentric) with the shock absorber for compression andrebound along the same axis. Pressure sensors and air pressure inlet andoutlet valves are connected to the computer for adjusting or regulatingthe pressure within the air spring to provide the desired spring rate.

The computer can be programmed so that the vehicle will provide anextremely smooth ride on level highways. Simultaneously, the computermay also be programmed so that only limited roll and pitch will beexperienced during cornering and/or braking while bumps encounteredduring cornering and/or braking will be cushioned significantly.Computer programming may also simultaneously provide the vehicle withgood off-road handling. Automatic load leveling may also be achieved. Insummary, virtually any suspension characteristics can be achieved byappropriate programming. Thus, the suspension system for a given vehiclemay provide an optimum set of ride and handling characteristics underall predictable conditions.

BRIEF DESCRIPTION OF THE DRAWING

The objects, advantages and features of this invention will be morereadily understood from the following detailed description when read inconjunction with the accompanying drawing, in which:

FIG. 1 is a diagrammatic illustration of a preferred embodiment of thesuspension system of the present invention;

FIG. 2 is a perspective view, with portions broken away, of a preferredembodiment of the combined shock absorber/air spring unit of thesuspension system of FIG. 1;

FIG. 3 is a schematic diagram of the combined shock absorber/air springunit of FIG. 2;

FIG. 4 is a basic block diagram of the control system of this invention;

FIG. 5 shows the inputs and outputs for one suspension unit;

FIG. 6 is a block diagram of the processing modules with their inputsand outputs;

FIG. 7 is a detailed block diagram for the processing module of a singlesuspension unit;

FIG. 8 is a simplified definitional diagram of a shock absorber;

FIG. 9 is a graphical representation of roll control for a predeterminedsegment of time;

FIG. 10 is a diagram for the forces, positions and velocities involvedin the topping out and bottoming out control functions;

FIG. 11 is a block diagram of one form of the control system of theinvention as applied to the structure of FIGS. 2 and 3;

FIG. 12 is an alternative arrangement for a controllable simple shockabsorber; and

FIG. 13 is another alternative embodiment similar to FIG. 12 but with ahigher performance shock absorber.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, in accordance with the present invention, a wheel10 is rotatably mounted on an axle 11 which extends from one end of acarrier 12. The other end of the carrier is pivotally mounted to theframe or chassis and body 14 of the vehicle. It should be understoodthat any wheel mounting approach may be used. A suspension unit 16 isconnected between chassis 14 and axle 11. Unit 16 combines an uppershock absorber 18 and a lower spring 20, which could be an air spring.The wheel, axle and carrier thus comprise the unsprung portion of thevehicle and the frame and body comprise the sprung portion of thevehicle. The damping forces of shock absorber 18 and the forces exertedby air spring 20 are varied by a control 22 in order to optimize theride and handling characteristics of the vehicle under a wide range ofdriving conditions.

Referring to FIG. 2 by way of example, shock absorber 18 and air spring20 of the suspension unit are arranged in series for simultaneouscompression and rebound along the same longitudinal axis as the wheel ofthe vehicle moves up and down with respect to the frame. The shockabsorber piston rod 24 extends axially through the center of air spring20 and is connected to the axle of the wheel. The air spring istypically made of a flexible bellows. A connecting member 26 extendsfrom the upper end of shock absorber 18 and is attached to the vehicleframe. The lower end of the air spring and rod 24 are interconnected ina known manner so that they move together.

An air tight cylindrical housing 28 concentrically surrounds shockabsorber 18. During compression and rebound of air spring 20, air flowsbetween the interiors of the air spring and housing 28 through a venthole 30 in base 32 of the housing. This air flow helps dissipate heatfrom the shock absorber. The size of the vent hole and air space inhousing 28 will affect the dynamic spring constant of air spring 20.Hydraulic fluid may be filled or drained from shock absorber 18 byremoving a fill plug 34 which normally seals a passage that extends fromthe shock absorber through base 32 of the housing.

Within housing 28 are mounted a hydraulic compression pressure regulator36 and a hydraulic rebound regulator 38. Also mounted within housing 28are an air pressure inlet valve 40 and an air pressure outlet valve 42.An air inlet nipple 44 and an electrical connection jack 46 are providedon or adjacent upper cap 48 of the housing. An air outlet nipple 50 isprovided on base 32 of housing 28. A resilient bump stop 25 is providedto protect the suspension on severe bumps.

Further details of an exemplary embodiment of suspension unit 16 willnow be described by way of reference to the schematic diagram of FIG. 3.Note that the computer control of this invention may operate with shockabsorbers of any suitable configuration, the only requirement being thatthey be controllable. Shock absorber 18 includes an inner cylinder 52and an outer cylinder 54 which surrounds the inner cylinder and definesa reservoir 56. A main piston 58 is connected to the upper end of pistonrod 24 and reciprocates longitudinally within inner cylinder 52. Piston58 divides inner cylinder 52 into an upper chamber 60 and a lowerchamber 62. Inner cylinder 52 and reservoir 56 of the shock absorber andall passages and chambers connected thereto are filled with a quantityof hydraulic fluid. There is no gas in contact with or in the fluid.

Piston 58 is slidable along the upper end of piston rod 24 between apair of fixed flanges 64 and 66 and is centered between the flanges bysprings 68 and 70. This resilient mounting of main piston 58 relative topiston rod 24 cushions any abrupt stops or starts of the piston, therebyeliminating the need for bleed valves in the main piston which are foundin conventional shock absorbers. No fluid is intentionally allowed topass between chambers 60 and 62 through piston 58.

While this is the presently preferred embodiment, because it allows thecomputer the maximum range of control over the compression and rebounddamping forces through regulators, it is to be understood that thecomputer control of this invention may operate with shock absorbershaving conventional valves in the main piston. Such an arrangement isdiscussed in connection with FIG. 12.

Shock absorber 18 is further provided with a compression amplifyingvalve 72 which is mounted above upper chamber 60. The function of thevalve 72 is described hereafter in greater detail. It includes a centralflanged spool 74 and an outer flanged spool 76 which reciprocates aboutspool 74. The reciprocation of these spools is limited by springs 78, 79and 80.

A hydraulic position sensor 82 communicates with reservoir 56 of theshock absorber. It includes a piston 84 which is moved by fluctuationsin the amount of hydraulic fluid within cylinder 52 due to the volumeoccupied by piston rod 24. Position sensor 82 also includes a transducersuch as a linear variable differential transformer 86. This transducergenerates signals representative of the position of piston 84 andtherefore the position of main piston 58. It is clear that with theposition of piston 58 known, the instantaneous relative positions of thesprung and unsprung masses are known.

Compression and rebound pressure regulators 36 and 38 may each compriselinear servo solenoid actuated valves. Signals may be applied to thesesolenoids to adjust the threshold blow off pressure required to openpassages 37 and 39 held closed by respective solenoid pistons 85 and 87.This provides a pressure regulator whereby predetermined pressureswithin chambers 61 and 62 can be independently selected by valves 36 and38, respectively. Fluid flow will be blocked until pressure reaches thepreselected threshold pressure, at which time the valve opens andattempts to maintain that pressure.

Similarly, air pressure inlet and outlet valves 40 and 42 may eachcomprise solenoid actuated valves. Signals may be applied to thesesolenoids to meter the flow of air therethrough. The function of airpressure inlet and outlet valves 40 and 42 is to adjust or regulate theair pressure within air spring 20. The control circuit applies signalsto the solenoids of these valves to meter the flow of air into and outof housing 28. This also adjusts the air pressure within air spring 20since the air can flow from within the housing and into the air springthrough vent hole 30. Air pressure inlet valve 40 is connected to apressurized gas source, such as an accumulator 94 which is in turnconnected to a pump 96. A pipe 98 connects the accumulator with inletnipple 44. This nipple communicates with valve 40 through a passage 100in cap 48. Air pressure sensors 99 and 101 generate signalsrepresentative of the air pressure within accumulator 94 and air spring20, respectively. Outlet orifice 102 of valve 40 communicates with theinterior of the housing. Inlet orifice 104 of air pressure outlet valve42 also communicates with the interior of housing 28. Passage 90 formedin base 32 of the housing connects the outlet of valve 42 to outletnipple 50. Passage 98 communicates the air pressure in accumulator 94with all of the suspension units associated with the different wheels ofthe vehicle.

Various passages such as 88 for hydraulic regulator 36 and 90 for outletvalve 42, which connect the aforementioned regulators and valves totheir fluid inputs and outputs, are formed in base 32 and cap 48 ofhousing 28. The leads such as 92 of the various solenoids are connectedto control 22 via electrical connector 46 (see FIG. 2). For example, thecontrol applies signals to the solenoids of regulators 36 and 38 toindependently adjust the pressure of the hydraulic fluid in upperchamber 61 and in lower chamber 62 to provide predetermined compressionand rebound damping forces. The pressure in chamber 61 sets thethreshold pressure in chamber 60 by way of the pressure amplifying valve72 to be described later. For purposes of this description the term"signals" will be used to include electrical signals or any other typewhich may be used to transfer information from one place to another inthis system.

The general operation of suspension unit 16 (FIGS. 2 and 3) can now bedescribed. When the unit undergoes compression and piston rod 24 movesupward, air spring 20 is compressed and energy is stored therein. Thepressure of the hydraulic fluid in chamber 60 increases as much aspressure regulator 36 allows via amplifying valve 72. This determinesthe compression damping forces. During rebound, air spring 20 expandsreleasing the stored energy. The pressure of the hydraulic fluid inchamber 62 increases as much as regulator 38 allows. This determines therebound damping forces.

Hydraulic fluid completely fills chambers 60 and 62 as well as reservoir56, the valves of regulators 36 and 38 and the passages leading to andfrom these valves. Hydraulic fluid also fills passage 106 leading topostion sensor 82. The housings of sensor 82 and valves 36 and 38 havevent holes 108 to permit the pressurized air which is within air spring20 and housing 28 to act on sides 85a and 87a of pistons 84, 85 and 87,respectively. The hydraulic fluid acts on the fluid side of the pistons84, 85 and 87, respectively. In this way, the shock absorber adds to thespring rate of the air spring due to its pressure on the fluid withinthe shock absorber. In addition, the action of the pressurized air onone side 84a, 85a and 87a of pistons 84, 85 and 87 provides a pressurebias to the hydraulic fluid which aids in preventing the formation ofgas bubbles or cavitation in the hydraulic fluid during reciprocation ofthe piston. A spring 400 can also be provided which acts on side 84a ofpiston 84 and adds to the pressure bias on the hydraulic fluid (FIG. 3).The lack of a spring on pistons 85 and 87 of the solenoids can beovercome by providing for the fluid in communication with the reservoir56 to completely surround the pistons 85 and 87 including the portionswithin the electrical coils (85a, 87a). Otherwise, an appropriate biasspring can be added to the pistons 85 and 87 to balance the fluidpressure resulting from spring 400. It is to be understood that,although the presently preferred embodiment employs both the action ofpressurized air and the action of spring 400 on side 84a of piston 84 toproduce a pressure bias on the hydraulic fluid, either could be usedalone or some alternate way of applying pressure to that side of piston84 could be adopted. Avoiding bubble formation in the hydraulic fluid isimportant to maintain good damping characteristics in that fluid.

During compression and rebound, position sensor 82 provides signals tocontrol 22 by means of leads 83 indicating the position of main piston58 within the shock absorber. The control uses this position informationto adjust regulators 36 and 38 as necessary to achieve predeterminedcompression and rebound damping forces. During compression, hydraulicfluid is pumped from upper chamber 60 of the shock absorber, throughamplifying valve 72 via passage 114 or 115 or both, and the valve ofregulator 36 and into reservoir 56. At the same time, hydraulic fluidfrom the reservoir is drawn through check valves 111 and into lowerchamber 62 of the shock absorber. The amount of fluid which is pumpedfrom upper chamber 60 and the amount of fluid which is pumped into lowerchamber 62 during compression is not equal. This is because of thevolume occupied by the portion of piston rod 24 which is progressivelyinserted into lower chamber 62 during compression. The extra hydraulicfluid moves piston 84 of the position sensor downwardly.

During rebound, hydraulic fluid is pumped from lower chamber 62, throughpressure regulator 38 and into reservoir 56. Hydraulic fluid is alsodrawn from reservoir 56 through check valves 110 positioned in a seatmember 112 of the compression amplifying valve 72 and into chamber 60.Piston 84 of position sensor 82 now moves upwardly since the volumeoccupied by the piston rod diminishes. The signals generated bytransducer 86 thus accurately represent the position of the main pistonwithin the shock absorber.

Compression pressure regulator 36 cannot adequately control exceedinglylow compression forces which may be required in upper chamber 60,because orifice 37 is too small for the amount of fluid that must flowfrom chamber 60 into reservoir 56 during rapid movement of piston 58.Therefore, compression amplifying valve 72 enables low compressiondamping forces to be generated, by providing sufficient orifice size forlarge flow rates at low compression damping forces, as may be desired.In addition, exceedingly high compression forces can be provided by thecompression amplifying valve at all flow rates.

Compression amplifying valve 72 operates as follows. As piston 58 startsto move upward, the pressure of the hydraulic fluid within chamber 60increases. Spring 79 keeps spool 74 against orifice 115 for a minimumpressure in chamber 60. Hydraulic fluid is forced through an orifice 114and check valve 116 in flanged spool 74 into upper chamber 61. Thepressure within chamber 61 is adjusted by compression pressure regulator36. If the pressure in chamber 61 is minimal, spool 76 rests againstseal 117, and spool 74 rests against seat 112. As the velocity of mainpiston 58 increases, pressure builds up against the flange of spool 74.Spring 79 determines the blow-off force required to displace spool 74upwardly. As spool 74 blows off, spring 80 is compressed.

As regulator 36 increases the pressure in upper chamber 61, spool 76 ispushed downwardly against springs 78 and 80. The force which pushesspool 76 downwardly is significantly greater than the force which pushesspool 74 upwardly, if chambers 60 and 61 are at similar pressure. Thisis because the area of the flange of spool 76 is significantly greaterthan that of spool 74. As spool 76 is pushed downwardly, the compressionof springs 78 and 80 increases the force required for blow-off of spool74 in such a manner as to set the threshold blow-off pressure in chamber60 via spool 74 to that of chamber 61 plus the preset bias pressure setby spring 79. This establishes a blow-ff pressure for spool 74 to thatset by pressure regulator 36 plus a small bias set by spring 79. Thisbias pressure insures that fluid flows through passage 114, openingcheck valve 116, and subsequently ensuring the proper operation ofregulator 36 and amplifying valve 72. Check valve 116 insures that thedesired pressure in chamber 61 as set by pressure regulator 36 remainsduring rebound (low pressure in chamber 60).

When the pressure in chamber 61 pushes spool 76 down to where spring 80is completely compressed, spring 80 no longer functions. Any increasedpressure in chamber 61 must be matched by several times that pressure inchamber 60 in order to blow-off flanged spool 74. This facilitates muchhigher pressure in chamber 60 than regulator 36 could produce. Properselection of the strength of springs 78, 79 and 80 with respect to oneanother is required in order to achieve the compression amplifyingfunction.

The rebound pressure regulator does not require the amplifying valvebecause the rebound speeds are more consistent since they deal primarilywith the natural frequency of the unsprung mass. This can be adequatelycontrolled by selection of the fixed size of passage 39 in combinationwith the variable threshold pressure set by pressure regulator 38. Inaddition, the rebound forces act differently on the chassis as affectingpassenger comfort in such a way as to allow larger forces in reboundwithout affecting comfort the way that similar compression forces would.

Having described the mechanical aspects of a somewhat complexcontrollable shock absorber and air spring, we will now turn to thecomputerized control system of this invention. It should be noted thatthe principles of the invention apply equally to vehicles having two ormore wheels with associated suspension units. Further, the principlesapply basically to a controllable damping device with or without acontrollable spring. That is, the controllable damping device of FIGS. 2and 3, or any other controllable damping device, can be employed withthe present system through the use of an air, leaf or coil spring, anyof which may not be controllable, as well as with the controllable airspring discussed above.

The basic block diagram shown in FIG. 4 represents a typicalfour-wheeled vehicle showing four controllable suspension units 202,204, 206 and 208 in communication with central processing unit 210. Eachsuspension unit may be of the form of FIGS. 2 and 3 or any othersuitable controllable device. Note that there are input and output linesbetween each suspension unit and the central processing unit. Thefunction and operation of each of these blocks will be discussed ingreater detail below.

The block diagram of FIG. 5 represents one of the suspension units ofFIG. 4 having four input signals and two output signals. F_(C) is thecontrol signal for setting the desired compression damping force andF_(R) is the control signal for setting the desired rebound dampingforce of the suspension unit. Each damping force is substantiallyindependent of the motion (velocity) of the axle with respect to thechassis. Stated another way, damping forces as controlled by thisinvention are substantially independent of velocity. The spring rateinputs of course apply to suspension units having controllable springssuch as shown in FIGS. 2 and 3. The inputs SR_(I) and SR_(D) are signalsthat control the increase or decrease, respectively, of the spring rate.On the output side of suspension unit 202 of FIG. 5 is the signal Prepresenting the position of the axle with respect to the chassis. Inactual physical terms, it is the position of the piston within the shockabsorber which is representative of the length of the shock absorberwhich, in turn, is representative of the actual position of the axlewith respect to the chassis. The K output is a signal representative ofthe spring rate which relates to the air pressure of the air spring.

The processing system of the present invention is shown in greaterdetail in FIG. 6. It is important to note that the position (P) andspring rates (K) for all of the suspension units are provided to aprocessing module associated with each suspension unit. Each processingmodule 212, 214, 216 and 218 has four outputs which are the inputs toeach suspension unit described above with reference to FIG. 5. Thesefour outputs set the desired spring rate and compression and rebounddamping forces in real time for optimum control and performance of eachof the suspension units independently but as a total composite toprovide for the desired ride characteristics of the vehicle. Even thougheach suspension unit is independently controlled by the processingmodules within the central processing unit, inputs from each suspensionunit to each independent processing module ensures that the compositeride of the vehicle is controlled

FIG. 7 is a detailed block diagram of the processing being performed byeach processing module associated with each suspension unit. In effect,the FIG. 7 diagram is equivalent to one processing module of FIG. 6. Theprocessing represented by FIG. 7 is the heart of the ability tooptimally control the suspension system. The nine basic parameters ofvehicle motion that are to be controlled and the manner in which theycan easily be simultaneously and optimally combined are shown in FIG. 7.It is possible that more than nine parameters may be involved, or lessfor certain applications.

The desired response of each suspension unit due to its involvement inthe various dynamics of the vehicle must be determined using appropriateconventional and easily understood mathematical algorithms. A set ofproposed algorithms are described herein for completeness indemonstrating how the process can function. These algorithms areexpository only and the invention is not limited to these particularmethods of calculation.

In general, all motions of the vehicle and its suspension units that areto be controlled are individually determined by using detectionalgorithms that generate a parameter that indicates to what extent thatmotion affects that suspension unit. As shown in the drawing, each ofthe nine dynamic characteristic detection blocks of the vehicle have oneor more output parameters representative of (PRO) that motion asaffecting the desired response of that particular suspension unit. Forexample, the values P and K from each suspension unit are input to rolldetection algorithm (DA) block 242, a total of eight inputs. The outputof DA 242 is a parameter representative of roll (PRO ROLL) which is thenacted upon by further processing blocks (244) that determine the desireddamping and spring rates required to control those particular states ofmotion. The desired responses to correct for roll (DR ROLL) are F_(C1)and F_(R1). This can be done by predetermined mathematical equations orby means of a stored digital memory table look-up, either determined andset by the manufacturer to provide the right control determined duringtesting of a vehicle, or by analysis.

Each compression and rebound damping force desired for each motion isadded together to give a composite and simultaneous resulting pair ofcompression and rebound damping forces desired by that suspension unit,thus providing the optimum control and response. This is because thesummation of the individually required control forces (ΣF_(C) ^(i) andΣF_(R) ^(i)) yields the total desired result in control forces withminimal degradation of individual desired results.

The height control or load leveling function has two parametersrepresenting states of motion. One indicates the condition of the roadsurface (PRO SURFACE), that is, smooth or bumpy, and the other indicatesthe average height of the vehicle above the road surface (PRO HEIGHT).Together, the desired response can be determined in such a way as toautomatically lower the vehicle for better aerodynamics on smooth roadssuch as freeways or raise it to go over bumpy roads more easily byallowing more chassis clearance above the road surface, thus providingan automatic adaptive load leveling function. Under normal conditions itwould be preferable to raise the chassis quickly when a bumpy surface isencountered, and lower it relatively slowly for a smooth surfaceaerodynamic advantages.

The signals F_(C) and F_(R) of FIG. 7 are representative of the desiredcompression and rebound damping forces as described above. If thesuspension units utilize signals that correspond almost directly to thedesired damping forces, such as the damping device shown in FIGS. 2 and3, then those F_(C) and F_(R) outputs are usable to control that dampingdevice directly through the appropriate interfaces. For visual referencepurposes, basic force/position relationships are shown in the diagram ofFIG. 8. Position parameter P is the instantaneous distance between themounts 230 and 232 of shock absorber 234. Compression forces result froma reduction in the value of P as the vehicle wheel moves toward thechassis, indicated by the upwardly directed arrow F_(C), and reboundforces act in the opposite direction as the wheel moves away from thechassis, represented by downwardly directed arrow F_(R).

Graphic illustrations of terms used in algorithms set out elsewhere inthis description are shown in FIG. 8. The difference from the normalmid-range of piston travel is ±D. The instantaneous position P_(ABS) isgiven by

    P.sub.ABS =P.sub.OFFSET -P.sub.ACT.

P_(OFFSET) is the distance between the chassis mount and the mid-rangeof piston travel and is a constant, while P_(ACT) is the actual positionof the piston.

The preferred embodiment of this invention as described herein issubstantially velocity independent with respect to the motion of thedamping device, that is, the motion between the axle and the chassis.However, the control system of this invention is adaptable to a velocitydependent suspension system. If the damping device has signal inputsthat do not directly control the damping forces, but are dependent onother conditions, then a conversion must be made. For example, if thedamping device involves velocity dependance, such as a situationresulting from incorporation of a servo-valve which controls the orificesize for control of the hydraulic fluid flow, then the damping force isdependent upon both the position signal and the velocity of the axlewith respect to the chassis. In that case, for any desired force, theproper signals must be translated for any given velocity at thatinstant. This may be accomplished by taking these signals representativeof the desired damping forces F_(C) and F_(R), and translating these toappropriate signals F'_(C) and F'_(R), which are a function of velocityand representative of the signals to provide the desired compression andrebound damping forces. This conversion is shown in FIG. 7 with optionalTRANSLATE blocks 236 and 238 coupled to the outputs of the processingmodule. Simply stated, the damping force resulting from hydraulic fluidflow through an opening is primarily a function of the size of theopening and the flow rate. If the size of the opening is set by thesignal and the flow rate is fixed by the velocity of the shock absorberpiston then, if the desired force and the piston velocity are known,there is a direct relationship to the desired signal (opening size) andit can be easily computed. Notice that the control signals will bechanging very rapidly with changing velocity and the damping device mustalso be able to respond with appropriate speed. In addition, thistranslation may be desired in the damping device that is substantiallyindependent of velocity (the structure of FIGS. 2 and 3) to furtheroptimize the control function.

In order to better understand the invention and its operation, it isappropriate to list a set of definitions and then to go through severaldetailed examples of the function of the system.

DEFINITIONS OF TERMS

"Spring Mass": this refers to the vehicle chassis which is mounted(sprung) on the suspension springs.

"Unsprung Mass": the wheel and axle supported by the road surface andfree to move (unsprung) with the road variations.

"Spring": an energy storage device which allows movement between chassisand wheel of the vehicle for maintaining an average force thatdetermines the average height of a chassis above the ground.

"Air Spring": a spring or energy storage device in which a flexiblecontainer holds air under pressure and attempts to change its size orlength resulting in less space for the air and a corresponding increasein the pressure resulting in an increase in force. Hence it provides aspring rate that is adjustable by changing the initial air pressure andthrough the design of its shape.

"Spring Rate": this refers to the change in force of the spring per unitlength of travel in pounds per inch when it is compressed. If offersstiffness to suspension movement so that higher rates means bettercontrol but a harsher ride.

"Shock Absorber": a damping device that helps to control the dynamicmotions of the spring, wheels and chassis but generating resistance torelative motions of the chassis and wheel through dissipation of energyby means of hydraulic fluid flow through a system of valves andorifices.

"Compression Force (F_(C))": the resistance to movement (pounds force)that the shock absorber produces when the wheel is moving toward thechassis.

"Rebound Force (F_(R))": the resistance to movement (pounds force) thatthe shock absorber produces when the wheel is moving away from thechassis.

"Roll": refers to the tilt sideways of a vehicle when cornering.

"Pitch": refers to the tilt forward or backward when a vehicle isbreaking, cornering or accelerating.

"Sprung Natural Frequency (SNF)": refers to the tendency of the sprungmass to oscillate on the springs when started in motion. The spring rateand vehicle weight determines the natural frequency of motion, typicallyabout 1 Hz.

"Unsprung Natural Frequency (UNF)": this refers to the tendency of theunsprung mass to oscillate between the springs and the road surfaceswhen started in motion. The spring rate and the wheel and axle weightdetermine the natural frequency of motion and are typically about 15 Hz.

"Stored Energy (SE)": the energy stored in a spring when compressed. Forpurposes of this invention, it refers to the energy in a suspensionspring when it has been compressed beyond its normal position, such aswhen a vehicle enters a steep driveway. The wheels compress upwardtoward the chassis when hitting the ramp and release that energy bycausing the front of the vehicle to rise sharply and then rock up anddown back to its normal position.

"Pumping Down (PD)": refers to a situation when the shock absorbercompression forces during rapid wheel movements are less than therebound forces such that the net or total resulting force on the chassisis predominantly downward, thereby overpowering the spring force andpulling the chassis lower to the ground so that there may beinsufficient clearance and bottoming out occurs.

"Bottoming Out (BO)": this refers to the condition where a bump or otherinfluence on the chassis or wheel causes the axle to try to rise towardthe chassis closer than it can physically, that is, to exceed thedynamic range of the travel of the suspension. This can cause a severejolt to the passengers and possibly damage the shock absorber orsuspension.

"Topping Out (TO)": this is the condition where a hole or otherinfluence on the chassis or wheel causes the axle to try to fall awayfrom the chassis further than it can physically, that is, exceed thedynamic range of the suspension's travel. This can possibly damage theshock absorber or suspension.

"Height Control": this refers to the adjustment of the overall averageheight of a chassis above the road surface. It is accomplished bychanging the air pressure in air springs or air pressurized load levelershock absorbers. Refer to the description of FIG. 8 above.

DEFINITIONS OF SYMBOLS

P_(ABS) : actual position of the piston (±D inches)

P_(MAX) : length of shock fully extended (-D inches)

P_(MIN) : length of shock fully compressed (+D inches)

P_(NORM) : average of P_(ABS) long term such as 30 seconds or more(inches)

P_(AVE) : short term (such as less than 15 seconds) average of P_(ABS)(inches)

P.sub.Δ : P_(ABS) -P_(NORM) (±D inches)

P_(H) : desired ride height (inches)

ΔP_(H) : height hysterisis (inches)

V_(ABS) : is P_(ABS) @t-P_(ABS) Εt-1 (inches per second)

DFT: Discrete Fourier Transform of P_(ABS) giving amplitude of unsprungnatural frequency (0 to D inches)

F_(C) : compression damping force desired

F_(R) : rebound damping force desired

Parameter with no prime: refers to suspension unit under control

Parameter with prime: refers to opposite side suspension unit from thatunder control

Parameter with double prime: refers to opposite end suspension unit fromthat under control

Parameter with triple prime: refers to diagonal suspension unit fromthat under control

Parameter with bar over: refers to maximum value desired

Parameter with bar under: refers to minimum value desired

ΔP_(ABS) ^(R) : P.sub.Δ -P'.sub.Δ (±2D inches)

ΔP_(ABS) ^(P) : P.sub.Δ -P".sub.Δ (±2D inches)

ΔP_(R) : is integrated roll position error (±2D inches)

ΔP_(P) : integrated pitch position error (±2D inches)

ΔP_(PD) : integrated pumped down position error (±D inches)

Δt: computational update period

N: number of bits resolution in a computer word

ΔR: incremental step for ΔP_(R) integration (inches)

ΔP: incremental step for ΔP_(P) integration (inches)

ΔPD: incremental step for ΔP_(PD) integration (inches)

ΔH: incremental step for ΔP_(H) integration (inches)

EXAMPLES

Some examples will be given to better illustrate how the actualequations will be utilized by the present invention to control thesuspension system of a vehicle. It should be recognized that thenumerical values that will be used are much larger than in actualpractice in order to simplify the examples. In addition, most of thecomputations are continuously being revised in real time so that arigorous development would be prohibitive here. However, the examplesshould be sufficient for a person skilled in the art to fully understandhow these examples would ultimately be applied to an actual system.

In general, a number of variables are recomputed or modified repeatedlyduring each successive computer cycle, a cycle being defined as thecomplete execution of all of the program algorithms. These cycles willbe performed about 250 times per second. Each cycle will generate somenew values and modify some previous values of the variables, thendetermine the desired composite compression forces, rebound forces andspring rates for all of the suspension units. These desired values wouldthen be output to the suspension units and held constant until thefollowing cycles modify them on a continuous basis.

The detailed equations are intended as an example of how the basicapplication of this invention would be implemented. Any equations thatperform according to the basic requirements of this invention may beused. A complete and rigorous "textbook" treatment of these commonmathematical equations would not add useful information in the contextof this specification. In order to fully, but simply, define theirusage, the first set of control equations for roll control will beaddressed in a detailed example in order to demonstrate how the processwill be performed. This will be followed by minimal comments for theremainder of the control algorithms, each of which requires similarcomputations. All of the equations involve commonly understoodmathematics.

ROLL CONTROL

A vehicle of three or more wheels is subject to roll when it leans tothe left or right such as during cornering or when subjected to crosswinds. The detection algorithms (DA) are based on the natural frequencyof the sprung mass. Approximately 100 ms integration of the actualposition with respect to the chassis is accomplished for all of thewheels. The difference between these integrated values for theparticular suspension unit under analysis and the one on the oppositeside indicates a roll condition. The determination of roll is done bycomparing front right to front left for the parameter representative offront right roll and front left to front right for the parameterrepresentative of front left control. This processing is repeated in thesame way for the rear. The integration averages out rapid changes inposition, such as during rapid bumps, and only changes in position atthe natural frequency of the sprung mass are detected.

The desired response (DR) for the suspension system is to reduce theamount of roll to which the chassis is subjected. If an axle is movingup toward the chassis due to roll, the compression damping force israised accordingly to limit this condition as it occurs. Likewise, ifthe axle is moving away from the chassis, the rebound force is raisedaccordingly to reduce this condition. Combined, two opposite axles beingcontrolled in this manner offer counter forces to those causing the rollcondition, thus greatly reducing the roll that would normally occur.This example is for the left front wheel only.

The following equations and calculations are performed for eachsuspension unit to derive its optimum control settings for each Δtperiod. The inputs to the detection algorithm portion of the processingmodule, ROLL DA block 242, are P_(ABS) and P'_(ABS). P_(ABS) is theposition P of the left front wheel provided by the position sensor andP'_(ABS) is the position P of the right front wheel provided by theposition sensor. Position P is the value P shown in FIG. 5. The range ofthe inputs is ±D inches and the resolution of these inputs is -2^(N-1)to +2^(N-1) steps at D/2^(N-1) inches per step. The intermediateequations are as follows:

    P.sub.NORM =Long term average of P.sub.ABS

    P'.sub.NORM =Long term average of P'.sub.ABS

    P.sub.Δ =P.sub.ABS -P.sub.NORM

    P'.sub.Δ =P'.sub.ABS -P'.sub.NORM

    ΔP.sub.ABS.sup.R =P.sub.Δ -P'.sub.Δ

    ΔP.sub.R @t=ΔP.sub.R @t-1+ΔR(if ΔP.sub.ABS.sup.R >ΔP.sub.R @t-1)

    ΔP.sub.R @t=ΔP.sub.R @t-1-ΔR(if ΔP.sub.ABS.sup.R <ΔP.sub.R @t-1)

The output of ROLL DA block 242 is ΔP_(R), the parameter representativeof roll (PRO ROLL). This becomes the input to the ROLL DR block 244which must determine the desired response for that roll condition.

The outputs of the processing module, ROLL DR block 244, will preferablybe determined from a look-up table in the processor memory and will beF_(C1) and F_(R1). The range of the output will be 0 to F_(C1) (maximumvaluue) for F_(C1), 0 to F_(R1) (maximum value) for F_(R1) and -2D to+2D for ΔP_(R). The resolution of the outputs will be: (1) 0 to 2^(N-1)steps at F_(C1) /2^(N-1) pounds per step for F_(C1) ; (2) 0 to 2^(N-1)steps at F_(R1) /2^(N-1) pounds per step for F_(R1) ; and (3) -2^(N) to+2^(N) steps at 2D/2^(N) inches per step for ΔP_(R).

Graphically, the outputs can be represented by the following:

                  TABLE I                                                         ______________________________________                                        ΔP.sub.R  F.sub.C1                                                                             F.sub.R1                                               ______________________________________                                         +2D                                                                                           ##STR1##                                                                             0                                                     ↑         ↑                                                                              ↑                                                0               0      0                                                      ↓        ↓                                                                             ↓                                                -2D             0                                                                                    ##STR2##                                              ______________________________________                                    

We will now provide a detailed description of the steps to be carriedout employing the equations provided for roll control in order to showhow and why the system accomplishes its purpose in limiting vehicle loadduring cornering. This example applies only to the left front wheel of astandard four-wheel vehicle. Total vehicle roll control will be providedonly when all four suspension units have had similar calculationsperformed and subsequent forces determined for each unit. In addition,these forces for roll control must be combined with all of the othercomputed forces for the other dynamic motions that the system iscontrolling before deriving a pair of composite compression and rebounddamping forces for that computer cycle, independently for each wheel.

For this example it will be assumed that the vehicle was travelling on astraight path and then was directed into a sharp right hand turn. Thisresults in forces that tend to cause the vehicle to roll to the left,subsequently causing the left front wheel to move up and closer to thechassis and the right front wheel to move further away from the chassis.The purpose of the roll control function is to apply the propercounteracting damping forces to greatly limit this roll as it occurs.The following steps will show how the desired counteracting dampingforces for the left front wheel would be computed, with the desiredforces for the remaining wheels to be determined in the same manner.

Step 1: Computation of P_(NORM)

For purposes of this computation, P_(ABS) is assumed to vary ±3 incheswith 0 inches being the approximate normal position when the vehicle isresting at its desired height on a flat surface, and P_(NORM) is thelong term average of P_(ABS) over about a 30-second period. Theprocedure for this step is that P_(NORM) is assumed to be 0, since thevehicle has been travelling straight over a road surface with any bumpsbeing averaged out, indicating that its desired height that was set bythe height control function has remained constant over long periods. Ifthis were not the case, the vehicle would be moving into the air or intothe ground, conditions which are not permitted. The height controlfunction may vary the value of P_(NORM), but the following algorithmscompensate for this automatically and still provide the desiredfunction. The applicable computations for Step 1 are:

P_(ABS) =any allowed value in inches

P_(NORM) =0 inches

Step2: Computation of P'_(NORM)

For this step, relating to the right front wheel, P'_(ABS) and P'_(NORM)are defined in the same way as their counterparts for the left frontwheel discussed above. The procedures and computations are also the sameso that

P'_(ABS) =any allowed value in inches

P'_(NORM) =0 inches

Step 3: Computation of P.sub.Δ

P.sub.Δ has previously been defined. The vehicle is assumed to havestarted a right turn so that it begins to lean or roll to the leftresulting in the left front wheel moving closer to the chassis. Assumingthat it is 1 inch closer, the computations are as follows:

    P.sub.ABS =+1 inch

    P.sub.Δ =P.sub.ABS -P.sub.NORM

    P.sub.Δ =+1-0=+1

Step 4: Computation of P'.sub.Δ

The definition of the symbols employed have previously been set forthand we now deal with the wheel on the opposite side of the one subjectto control, in this case, the right front wheel. The same explanation asthat for Step 3 applies except that cornering is resulting in chassismovement upward on the right side so that the right front wheel is nowsummed to be 1 inch further from the chassis, with the followingcalculations:

    P'.sub.ABS =-1 inch

    P'.sub.Δ =P'.sub.ABS -P'.sub.NORM

    P'Δ=-1-0=-1

Step 5: Computation of ΔP_(ABS) ^(R)

This computation is to indicate the direction and extent that thevehicle could be rolling. The term ΔP_(ABS) ^(R) applies to the leftfront wheel but it is derived from information about both front wheels.Since P'.sub.Δ for the opposite side is subtracted from P.sub.Δ for thewheel under control, the result indicates the direction and amount ofroll that affects the left front wheel. Note that P_(ABS) and P'_(ABS)are changing with each computer cycle as the wheel moves. Therefore,P.sub.Δ and P'.sub.Δ are also changing. For this reason, ΔP_(ABS) ^(R)only indicates the possible direction of roll at that particular time t.The road surface irregularities at each cycle could indicate differentroll conditions. However, since the vehicle must maintain an overallequilibrium, that is, it must not ride sideways for very long beforerighting itself due to the springs, the actual condition of roll can beextracted by a type of digital filtering or integration as will be shownin subsequent computations. The computations for this step are:

    ΔP.sub.ABS.sup.R =P.sub.Δ -P'.sub.Δ

    ΔP.sub.ABS.sup.R =(+1)-(-1)

    ΔP.sub.ABS.sup.R =+2 inches

Step 6: Computation of ΔP_(R)

For purposes of this step, Δ_(R) is the predertermined constant ofintegration that determines the response of the filter (integration); trefers to time as indicated by one of the computer cycles and t-1 is theprevious computer cycle; ΔP_(R) is the parameter indicating thedirection and extent that the vehicle is actually rolling as extractedfrrom ΔP_(ABS) ^(R). The integration equations employed for this steprequire a decision as to whether the instantaneous roll indication(ΔP_(ABS) ^(R)) is greater or less than the previously computed actualroll indication (ΔP_(R)). If roll is indicated to be greater than theprevious value of actual roll (ΔP_(ABS) ^(R) >ΔP_(R) @t-1), then theintegration constant (Δ_(R)) is added to increase the estimate of actualroll. If roll is indicated to be less than the previous value of actualroll (ΔP_(ABS) ^(R) <ΔP_(R) @t-1), then the integration constant (Δ_(R))is subtracted to decrease the estimate of actual roll. Given thecomputation involved with this parameter, it is clear that if the wheelsare randomly moving over bumps, the additions and subtractions willcancel, indicating no roll is occurring, that is, ΔP_(R) =0. If,however, the vehicle is starting to roll, the additions and subtractionswill not offset and the direction and amount of roll will be indicated,that is, ΔP_(R) ≠0. In the present example for a right turn, the leftfront wheel is on average remaining closer to the chassis while theright front wheel is on average remaining further from the chassis.

For this computation, the integration constant will be assumed to be 0.5inch, Further, since the vehicle was on a straight path prior to theright turn, the actual roll indication at the start of the turn is 0,that is, ΔP_(R) @t-1=0. From the prior discussion, ΔP_(ABS) ^(R) wascomputed to be +2 inches. Since this is greater than 0(ΔP_(ABS) ^(R)>P_(R) @t-1), 0.5 inches will be added to the actual roll indication(ΔP_(R) @t=ΔP_(R) @t-1+ΔR). We have already defined ΔP_(R) for theconditions of ΔP_(ABS) ^(R) increasing or decreasing. The computationsinvolved in this step are as follows:

    Δ.sub.R =0.5 (constant)

    ΔP.sub.R @t=ΔP.sub.R @t-1+ΔR

    ΔP.sub.R @t=0+0.5=0.5 inches

Step 7: Computation of F_(C1) and F_(R1)

The fact that roll is occuring is now known by the computation of ΔP_(R)and the appropriate counteracting damping forces can be derived fromthat value by using predefined equations that must be processed. Afaster and preferred approach is to use a table look-up within theprocessor memory. A digital memory contains all possible damping valuesstored at address locations that are related to the extent and directionof roll. When a new ΔP_(R) is derived, its value indicates where to goin the stored memory table to get the desired damping values. Such atable would be preprogrammed and easily changeable as desired by thevehicle manufacturer for the desired performance. An actual table wouldhave about 256 entries, ΔP_(R) would be tabulated in hundredths of inchsteps, and the damping forces would vary only a few pounds per step formuch greater control and accuracy than provided in the example tableshown below.

                  TABLE II                                                        ______________________________________                                        P.sub.R        F.sub.C1 F.sub.R1                                              ______________________________________                                        +2.0 inches    400 lbs. 0 lbs.                                                +1.5 inches    300 lbs. 0 lbs.                                                +1.0 inches    200 lbs. 0 lbs.                                                +0.5 inches    100 lbs. 0 lbs.                                                +0.0 inches    0 lbs.   0 lbs.                                                -0.5 inches    0 lbs.   100 lbs.                                              -1.0 inches    0 lbs.   200 lbs.                                              -1.5 inches    0 lbs.   300 lbs.                                              -2.0 inches    0 lbs.   400 lbs.                                              ______________________________________                                    

From the table, the desired damping forces to control the indicated rollfor the left front wheel during this particular computer cycle is

    F.sub.C1 =100 lbs

    F.sub.R1 =0 lbs

It is important to know that F_(C1) and F_(R1) apply to the left frontwheel and are for roll control only. By appropriate redefinition ofP'_(ABS) -P_(ABS), etc., similar damping values for the other threewheels can be computed. These values are temporarily stored whileappropriate damping forces to control the other dynamics, that is,pitch, stored energy, etc., are also computed and stored during anygiven computer cycle. At the end of the cycle, the appropriate compositeforces are determined by adding the individual forces and these areprovided to the mechanical suspension units and held until the nextcycle is completed and the values are replaced by the revised values. At250 cycles per second, the damping forces become uniform andcontinuously varying functions that can provide near optimumperformance.

If many examples of the above process were repeated, it would becomeclear that ΔP_(R) is continuously revised and always returns to 0 incheswhen the vehicle is not subject to roll. That is, for roll control, thealgorithm keeps providing damping forces to counteract roll forces asthey occur, and no forces when the vehicle is level, as desired.

It can be seen that ΔP_(R) is essentially a form of real timeintegration of a time-varying function that detects slow positionalchanges. The update period and the value of Δ_(R) set the bounds on therate that position changes are detected. This allows the computer toignore rapid variations such as bumps and holes. Since it is known thatthe natural frequency of the sprung mass limits the rate at which thechassis can roll, a proper choice for Δ_(R) and cycle time can bedetermined, despite rapid momentary fluctuations of the wheel due toroad surface conditions.

A graphical demonstration of roll control is provided by FIG. 9. It isassumed that the vehicle is following a straight path and then is goinginto an S curve with a right turn followed by a left turn. It is alsoassumed that the road is relatively bumpy. Without rigorouscalculations, using the above algorithms as described, a graphicalrepresentation of the variations of P.sub.Δ, P'.sub.Δ, ΔP_(ABS) ^(R) andΔP_(R) are shown, along with the resultant F_(C1) and F_(R1) signals. Ifthe whole process of travelling through the curves took 5 seconds, theabove algorithms would have been repeated 250×5 or 1,250 times. Thisgraphical example shows the general process that would occur in such ahypothetical case. It should be remembered that this example is for leftfront wheel roll control only and it does not incorporate otherparameters nor does it refer to the control of the other wheels.

From FIG. 9 it can be seen that a bump or a hole encountered while thevehicle is on the initial straight path is filtered out and results inno damping forces F_(C1) or F_(R1) being generated. The first two curvesrepresent the two front wheel positions and ΔP_(ABS) ^(R) is thedifference between them. The integrated value ΔP_(R) follows thedifference. Compression force F_(C1) is applied to the left front wheelin the right turn, and F_(R1) is applied to that wheel in a left turn.

PITCH CONTROL

The term pitch has been previously defined and applies to a vehicle withtwo or more wheels when it leans forward or backward as in braking,acceleration or cornering. The detection algorithms and desired responseare substantially the same as for roll control except that the frontwheel is compared to the rear wheel on the same side instead of beingcompared with the opposite wheel on the same end.

The inputs to the processing module PITCH DA block 246 are P_(ABS) andP"_(ABS). The range of the inputs is ±D inches and the resolution ofthese inputs is -2^(N-1) to +2^(N-1) steps at D/2^(N-1) inches per step.The intermediate equations are as follows:

    P.sub.NORM =Long term average of P.sub.ABS

    P".sub.NORM =Long term average of P".sub.ABS

    P.sub.Δ =P.sub.ABS -P.sub.NORM

    P".sub.Δ -P".sub.ABS -P".sub.NORM

    ΔP.sub.ABS.sup.P =P.sub.Δ -P".sub.Δ

    ΔP.sub.P @t=ΔP.sub.P @t-1+ΔP(if ΔP.sub.ABS.sup.P >ΔP.sub.P @t-1)

    ΔP.sub.P @t=ΔP.sub.P @t-1-ΔP(if ΔP.sub.ABS.sup.P <ΔP.sub.P @t-1)

Again, ΔP_(P) is the output of PITCH DA block 246 going into PITCH DRblock 248; which must determine the desired response for the pitchcondition.

The outputs of the processing module PITCH DR block 248 will preferablybe determined from a look-up table in the processor memory and will beF_(C2) and F_(R2). The range of the output will be 0 to F_(C2) (maximumvalue) for F_(C2), 0 to F_(R2) (maximum value) for F_(R2) and -2D to +2Dfor ΔP_(P). The resolution of the outputs will be: (1) 0 to 2^(N-1)steps at F_(C2) /2^(N-1) pounds per step for F_(C2) ; (2) 0 to 2^(N-1)steps at F_(R2) /2^(N-1) pounds per step for F_(R2) ; and (3) -2^(N) to+2^(N) steps at 2D/2^(N) inches per step for ΔP_(P).

Graphically, the outputs can be represented by the following:

                  TABLE III                                                       ______________________________________                                        ΔP.sub.P  F.sub.C2                                                                             F.sub.R2                                               ______________________________________                                         +2D                                                                                           ##STR3##                                                                             0                                                     ↑         ↑                                                                              ↑                                                0               0      0                                                      ↓        ↓                                                                             ↓                                                -2D             0                                                                                    ##STR4##                                              ______________________________________                                    

Pitch control is handled almost identically with that of roll controlexcept that the differences are measured between front and rear wheels,that is, in braking the left front wheel moves closer to the chassiswhile the left rear wheel moves farther from the chassis. A differentconstant of integration, ΔP, is used but otherwise the procedure is thesame as that for roll control with each individual suspension unit beingprocessed appropriately. The detection algorithms PITCH DA block 246provides the parameter representative of pitch to desired response block248 (PITCH DR) which determines the damping forces necessary (F_(C2) andF_(R2)).

STORED ENERGY AND SPRUNG NATURAL FREQUENCY

Although independent processes, these control algorithms have beengrouped together because of their similarity and relationship. The basiccontrol processes given counteract the spring forces that act on thechassis due to changes in the axle positions with respect to the normalposition or equilibrum. In addition, the stored (spring) energy cancause motions at the sprung natural frequency in two different ways.Therefore although the equations have been grouped together, each of thetwo will be separately addressed after the inputs, equations and outputshave been specified.

The inputs to the processing module are P_(ABS), P'_(ABS), P"_(ABS) andP"'_(ABS). The range of the inputs is ±D inches and the resolution ofthese inputs is -2^(N-1) to +2^(N-1) steps at D/2^(N-1) inches per step.The intermediate equations are as follows:

    P.sub.NORM =Long term average of P.sub.ABS

    P'.sub.NORM =Long term average of P'.sub.ABS

    P".sub.NORM =Long term average of P".sub.ABS

    P"'.sub.NORM =Long term average of P"'.sub.ABS

    P.sub.Δ =P.sub.ABS -P.sub.NORM

    P'.sub.Δ =P'.sub.ABS -P'.sub.NORM

    P".sub.Δ =P".sub.ABS -P".sub.NORM

    P'".sub.Δ =P'".sub.ABS -P'".sub.NORM

The output of the processing module will preferably be determined from alook-up table in the processor memory and will be F_(C3), F_(C4),F_(C5), F_(C6), F_(R3), F_(R4), F_(R5) and F_(R6). The range of theoutput will be 0 to F_(Ci) for F_(Ci) and 0 to F_(Ri) for F_(Ri) wherei=3, 4, 5, 6, and -D to +D for P.sub.Δ^(K) where K=, ', ", "'. Theresolution of the outputs will be: (1) 0 to 2^(N-1) steps at F_(Ci)/2^(N-1) pounds per step for F_(Ci) ; (2) 0 to 2^(N-1) steps at F_(Ri)/2^(N-1) pounds per step for F_(Ri) ; and (3) -2^(N-1) to +2^(N-1) stepsat D/2^(N-1) inches per step.

SPRUNG NATURAL FREQUENCY

This term has been defined previously. The detection algorithm could bea Discrete Fourier Transform Analysis, a well-known mathematicalprinciple. However, it is desired that only one cycle of oscillation bepermitted and therefore, a direct look at the position and movement ofthe axle with respect to the chassis is most desirable. This willindicate if the sprung mass is oscillating. The response desired forthis parameter is that the suspension unit under analysis be controlledby applying a rebound force as it is compressed sp that it will returnto its equilibrium position, but the rate of return will be slowed andsome of the stored energy will be dissipated in the flow of hydraulicfluid through the valves. Likewise, as the spring is extended, thecompression force is applied to slow the rate of return and dissipatethe stored energy.

As in the other examples, the sprung natural frequency control processcorresponds only to the suspension unit under control. If the axle andwheel corresponding to this unit is pushed upward above normal by a risein the road surface, the compressed spring that exerts an upward forceon a chassis will tend to cause the chassis to rise up at its naturalfrequency and potentially oscillate up and down. By applying acounteracting positive rebound damping force proportional to the amountof spring compression and spring rate, this oscillation can beeffectively damped. In other words, the combination of the increasedupward spring force and counteracting rebound damping force result in anear neutral force upward on the chassis, consequently preventing anysprung natural frequency oscillations and providing a level and smoothride. A predefined amount of spring force will always be allowed toremain in order to allow the chassis to recover or return to its propernormal position within a desired amount of time, that is, the rebounddamping does not effectively lock the spring at some compressedposition.

It will be observed that the computation look-up tables for compressionand rebound damping forces include a negative force in addition to apositive force, which is proportional to the spring compression. This isprovided to allow for the additional upward force caused by the springcompression when summing the desired compression forces on the othercontrol functions such as roll, pitch, etc. In other words, if rollcontrol has determined the need for 100 lbs of compression force and thesprung natural frequency indicates that the spring is contributing anadditional upward force of 100 lbs due to compression, the two willmathematically cancel for an optimum net composite upward force on thechassis at the end of the computer cycle. A spring extension belownormal, such as when the wheel drops onto a lowered road surface or intoa hole, is similarly handled with a positive compression force tocompensate for the loss of upward spring force, and a negative reboundforce to counteract other required rebound forces as similarly describedfor a bump.

STORED ENERGY

Although this term has previously been defined additional comments areappropriate. For this function, stored energy is the difference betweenthe compressed force for equilibrium and the actual compressed force,and its effect on the sprung mass. For example, if a point on a vehicleis compressed down, it will tend to rise back up and, if raised, it willtend to drop back down. These forces act on the vehicle as a whole.Thus, if the front wheels are compressed upward by a bump, the rear ofthe vehicle will tend to move downward due to the resulting torque aboutthe center of gravity of the vehicle. Therefore, all of the suspensionunits controlled by this invention must be considered as to theirposition relative to the equilibrium position.

For the detection algorithms, the conditions can be determined easily bycomparing the change in position of the axle with respect to the chassiswith the position at equilibrium.

With reference to the desired response, it is useful to know that all ofthe suspension units other than the one under control can influence thesuspension unit under control, due to their stored energy, if they arenot in their equilibrium position. For this reason that portion of theprocessing module relating to stored energy is enclosed with a dottedbox 250 to indicate that the signals relate to the other suspensionunits but not the one under analysis. The effect of the other units iscounteracted by the stored energy function by applying the correctcounterdamping. For example, if a front suspension unit is compressed,it will tend to push up the front and cause a torque around the centerof gravity of the vehicle and tend to compress the rear downwardly.Therefore, compression force would be increased on the rear. Likewise,rebound force would be increased on the rear in response to an extensionof a suspension unit in the front.

The stored energy control process is included in this control system tohandle forces on the suspension unit under control due to spring forcesimposed on the rest of the chassis caused by road conditions. Theoperation is similar to attempting to maintain constant forces on thechassis, only the compression and rebound damping forces must act inopposite directions to counteract the forces on the chassis. In otherwords, if the front of the vehicle hits a rise in the road surface andthe front springs are compressed, their upward force will tend to applya torque to the vehicle tending to compress the rear springs. When therear spring is under control, the proportion of compression on the frontsprings will result in increased damping force to counteract this torqueand prevent the rear from sinking.

The stored energy and sprung natural frequency control functions tend tocontrol the forces that act on a chassis due to road surface variationscompressing and extending the spring and consequently applying forces tothe chassis that would normally tend to move the chassis off its desiredlevel ride. It should be noted that since the spring rates may vary dueto level control for varying loads, the spring rate inputs may be usedto modify the effective spring displacement so that optimumcounteracting forces can be applied at all times. For the purposes offurther illustration, tables IV-VII show the range of outputs for thesetwo parameters.

                  TABLE IV                                                        ______________________________________                                        P.sub.Δ  F.sub.C3                                                                              F.sub.R3                                               ______________________________________                                         +D                                                                                           ##STR5##                                                                              ##STR6##                                              ↑        ↑ ↑                                                0              0       0                                                      ↓       ↓                                                                              ↓                                                -D                                                                                           ##STR7##                                                                              ##STR8##                                              ______________________________________                                    

                  TABLE V                                                         ______________________________________                                        P'.sub.Δ F.sub.C4                                                                              F.sub.R4                                               ______________________________________                                         +D                                                                                           ##STR9##                                                                              ##STR10##                                             ↑        ↑ ↑                                                0              0       0                                                      ↓       ↓                                                                              ↓                                                -D                                                                                           ##STR11##                                                                             ##STR12##                                             ______________________________________                                    

                  TABLE VI                                                        ______________________________________                                        P".sub.Δ F.sub.C5                                                                              F.sub.R5                                               ______________________________________                                         +D                                                                                           ##STR13##                                                                             ##STR14##                                             ↑        ↑ ↑                                                0              0       0                                                      ↓       ↓                                                                              ↓                                                -D                                                                                           ##STR15##                                                                             ##STR16##                                             ______________________________________                                    

                  TABLE VII                                                       ______________________________________                                        P"'.sub.Δ                                                                              F.sub.C6                                                                              F.sub.R6                                               ______________________________________                                         +D                                                                                           ##STR17##                                                                             ##STR18##                                             ↑        ↑ ↑                                                0              0       0                                                      ↓       ↓                                                                              ↓                                                -D                                                                                           ##STR19##                                                                             ##STR20##                                             ______________________________________                                    

PUMPING DOWN

This term has previously been defined. The detection algorithms involvea short term integration (about 3 seconds) of the position of the axlewith respect to the chassis and that is compared to the long termaverage (about 30 seconds) to detect if the position is pumping down.The response is that as the suspension unit starts to pump down, thecompression force is correspondingly increased to balance the dampingand limit the amount of pumping down that can occur.

The input to the processing module is P_(ABS). The input range is ±Dinches and the resolution of the input is -2^(N-1) to +2^(N-1) steps atD/2^(N-1) inches per step. The intermediate equations are as follows:

    P.sub.NORM =Long term average of P.sub.ABS

    P.sub.Δ =P.sub.ABS -P.sub.NORM

    ΔP.sub.PD @t=ΔP.sub.PD @t-1+Δ.sub.PD (if P.sub.Δ >ΔP.sub.PD @t-1)

    ΔP.sub.PD @t=ΔP.sub.PD @t-1-Δ.sub.PD (if P.sub.Δ <P.sub.PD @t-1)

The outputs of the processing module will preferably be determined froma look-up table in the processor memory and will be F_(C7) and F_(R7).The range of the outputs will be 0 to F_(C7) for F_(C7), 0 to F_(R7) forF_(R7) and -D to +D for ΔP_(PD). The resolution of the outputs will be:(1) 0 to 2^(N-1) steps at F_(C7) /2^(N-1) pounds per step for F_(C7) ;(2) 0 to 2^(N-1) steps at F_(R7) /2^(N-1) pounds per step for F_(R7) ;and (3) -2^(N-1) to +2^(N-1) steps at D/2^(N-1) inches per step forΔP_(PD).

Graphically, the outputs can be represented by the following:

                  TABLE VIII                                                      ______________________________________                                        P.sub.PD        F.sub.C7                                                                             F.sub.R7                                               ______________________________________                                         +D                                                                                            ##STR21##                                                                            0                                                     ↑         ↑                                                                              ↑                                                0               0      0                                                      ↓        ↓                                                                             ↓                                                -D              0                                                                                    ##STR22##                                             ______________________________________                                    

Pumping down is controlled by integrating the average height of asuspension unit over a period of time longer than the naturalfrequencies of the sprung mass but shorter than the computation of theaverage height (ΔP_(PD)). It includes an integration of the change inheight computed just as for roll or pitch control, only the actualchange in height from normal for any suspension unit under control isused instead of the difference between two suspension units.

UNSPRUNG NATURAL FREQUENCY

The detection algorithms employ Discrete Fourier Transform (DFT)analysis to determine the amplitude of the frequency component at thenatural frequency of the unsprung mass. The desired response is thatoscillations should be critically damped. The best approach appears tobe to increase compression damping as the oscillation amplitudeincreases to limit the level allowed and maintain good road traction byallowing easy rebound to keep the wheel on the surface, while preventingthe wheel from bouncing off the surface by increased compressiondamping.

The input to the processing module is P_(ABS) with a range of ±D inches.The resolution of the input is -2^(N-1) to +2^(N-1) steps at D/2^(N-1)inches per step. The intermediate equation is a DFT for frequency of theunsprung mass.

The output of the processing module will preferably be determined from alook-up table in the processor memory and will be F_(C8). The outputrange will be 0 to F_(C8) (maximum value) for F_(C8) and 0 to ±D forDFT. The resolution of the outputs will be: (1) 0 to 2^(N-1) steps atF_(C8) /2^(N-1) pounds per step for F_(C8) ; and (2) 0 to 2^(N-1) stepsat D/2^(N-1) inches per step for DFT.

The DFT analysis will operate in such a manner that each computer cyclewould store the instantaneous position of the axle with respect to thechassis and drop an older measurement, the older measurement being aninput value of position taken about 32 cycles previously. The computerwould then contain the latest 32 position readings at all times. If aDFT is taken each cycle on those points in order to determine themagnitude of any oscillations at or near the natural frequency of theunsprung mass, then that DFT output would represent the magnitude of anyunsprung natural frequencies that may be occurring, which is a basicfunction of a DFT. If compression damping is applied at increasing ratesas the natural frequencies are detected, that is, the DFT output, thenthe energy in the resident system would be effectively dissipated andany wheel hop or loss of control would be substantially reduced oreliminated.

Since the load leveling function changes the spring rates, the effectivevalue of the DFT could be appropriately modified to compensate for thischange in spring rate or natural frequency, based on the spring rateinput to the controller. The following table shows the range of outputsfor unsprung natural frequency.

                  TABLE IX                                                        ______________________________________                                                DFT  F.sub.C8                                                         ______________________________________                                                 D                                                                                  ##STR23##                                                               ↑                                                                            ↑                                                                  0    0                                                                ______________________________________                                    

BOTTOMING OUT AND TOPPING OUT

Here again the analysis of two functions have been combined due to theirsimilarity and relationship. Bottoming out is associated with chuckholes or excessive rebound travel while topping out is associated withhigh amplitude bumps or excessive compression travel. These terms havepreviously been defined.

Desired response for bottoming out is that this control functioncomputes the velocity of the axle with respect to the chassis and itsabsolute position. It has been stated previously that the present systemis velocity-independent but it should be noted that because the computercycles are much faster than physical changes in the automobile, velocitycan be computed from position inputs at any time desired. A desiredresponse for the bottoming out parameter is that the compression dampingforce is progressively increased as the suspension unit approaches itsminimal length to prevent any damage. The magnitude of the compressionforce is higher with higher velocity in order to bring the velocity tozero before bottoming out. This increasing force will help lift thechassis so that it can clear obstacles on a rough terrain.

The desired response for topping out is that the rebound damping forceis progressively increased as the suspension unit approaches its maximumlength to prevent damage. The magnitude of the rebound force is higherwith higher velocity in order to bring the velocity to zero beforetopping out. Thus it can be seen that these two control functions areclosely related, one being effectively the mirror image of the other.

The input to both processing modules is P_(ABS) with a range of ±Dinches and a resolution of -2^(N-1) to +2^(N-1) steps at D/2^(N-1)inches per step. The intermediate equation is

    V.sub.ABS =P.sub.ABS @t-P.sub.ABS @t-1.

The outputs of the processing modules will preferably be determined froma look-up table in the processor memory and will be F_(C9) and F_(R9).The range of the output will be 0 to F_(C9) (maximum value) for F_(C9),0 to F_(R9) (maximum value) for F_(R9) and -V_(ABS) to +V_(ABS) forV_(ABS). The resolution of the outputs will be: (1) 0 to 2^(N) steps atF_(C9) /2^(N) pounds per step for F_(C9) ; (2) 0 to 2^(N) steps atF_(R9) /2^(N) pounds per step for F_(R9) ; and (3) -2^(M) to +2^(M)steps at V_(ABS) /2^(M) inches per second per step for V_(ABS).

This control process independently increases compression damping as theaxle approaches bottoming out and increases rebound damping as the axleapproaches topping out. In other words, as the shock absorber or dampingdevice is approaching its minimum compressed length during a bump, thecontroller monitors the position and velocity of the axle with respectto the chassis, and increases the compression damping force to whateverlevel is required to stop the movement before bottoming out can occur.This is of course limited by the design limits of the compression forceand in the case of a large bump, it forces the mass of the vehicle upand over the obstacle with a smooth and evenly controlled force. Reboundcontrol likewise increases the rebound damping force to prevent the axlefrom approaching its maximum extension from the chassis without firstbringing it to a stop, also smoothly. The diagram of FIG. 10 shows thebottoming out and topping out control function dynamics. Note that asposition increases left or right from the center line, the compressionforce increases but only with increased velocity. Thus there are twoparameters, and either one can be increasing in order to increase thecompression force. At greater velocities the force increases at muchsmaller position changes to allow time to smoothly decelerate the axle.Likewise the rebound force on the negative side of the position andvelocity also increases with those two parameters value increases.

HEIGHT CONTROL

This is often referred to as load leveling and is the long term increaseor decrease of the spring rate to keep the sprung mass at a desiredaverage height above the road surface. It functions with a controllablespring such as the air spring shown in FIGS. 2 and 3. This function usesthe long term average position of the axle with respect to the chassisand the absolute position. The algorithm provided allows for adaptivecontrol of the height of each suspension unit so that variations inheight between the front and rear of the vehicle can be accommodated forsuch things as to aid in aerodynamics for fuel economy, or to raise thechassis for improved clearance when going over bumpy roads.

The desired response of the height control function is to provideadaptive load levelings so that on smooth roads, such as freeways, thevehicle lowers for improved aerodynamics. When a rough road or bumps areencountered, it automatically raises to a height that offers sufficientdynamic range for the bumps. The maximum values of the absolutepositions as they occur, that is, its peaks above normal, indicate thesurface, and the height can then be adaptively adjusted to allow thedesired dynamic range for covering the road surface.

The input to the processing module is P_(ABS) with a range ±D inches anda resolution of -2^(N-1) to +2^(N-1) steps at D/2^(N-1) inches per step.The intermediate equations are as follows:

    If P.sub.Δ (any wheel)>H, then H@t=H@t-1+KΔ.sub.H

    If P.sub.Δ (any wheel)≦H, then H@t=H@t-1-Δ.sub.H (H≧0)

    P.sub.AVE =Average of P.sub.ABS

The output of the processing module will preferably be determined from alook-up table in the processor memory and will be P_(H), the desiredheight. The actual outputs SR_(I) and SR_(D) will serve to adjust forthat height. If P_(AVE) >P_(H) +ΔP_(H), supply pressurized air to airspring until P_(AVE) <P_(H), at which time check for P_(AVE) >P_(H)+ΔP_(H) before adding further pressure. If P_(AVE) <P_(H) -ΔP_(H),release air from air spring until P_(AVE) >P_(H), at which time checkfor P_(AVE) <P_(H) -ΔP_(H) before releasing air again. Graphically, theoutputs can be represented by the following:

                  TABLE X                                                         ______________________________________                                                H    P.sub.H                                                          ______________________________________                                                0    0                                                                        ↓                                                                           ↓                                                                 +D   -D                                                               ______________________________________                                    

In this function, one or more axle positions are monitored each computercycle with respect to the normal chassis position. A type of integrationsimilar to that of the roll control function is then implemented whichgenerates an intermediate signal (H) that is representative of the sizeof bumps encountered (SURFACE in FIG. 7). In the integration we add Ktimes ΔH where ΔH is the constant of integration. As the bumps becomesmaller, the value of H decreases more slowly where we add only ΔH inthe integration. This is because when bumps are first encountered, thechassis must be raised fairly rapidly to allow proper clearance forfuture bumps that could be expected. When no bumps are encountered, thechassis will slowly lower to optimum ride height as previouslydescribed.

The desired ride height obtained from the look-up table in the processorfor a given H is processed with hysteresis ΔP_(H) so that the control ofthe spring rate doesn't keep changing too rapidly between increasing anddecreasing commands, thereby resulting in smoother control. In otherwords, the chassis will rise up adaptively to accommodate bumps andautomatically lower when no bumps are encountered.

SUMMARY OF EXAMPLES

The preceding examples have been provided to demonstrate how the givenalgorithms may be implemented and why they control the dynamicsspecified. At the end of each computer cycle, a desired compression andrebound damping force, as well as a string rate control parameter, havebeen computed for each suspension unit and for each control functionsuch as roll, pitch, etc. Each suspension unit is capable of only onecomposite rebound or compression force so that the desired forces mustbe appropriately combined to form the optimum compression and reboundforces. The well-known mathematical principle of superposition applieshere. A number of individual parameters, each separately calculated, areadded directly to form a sum or composite that provides the properresult for each as a total. Therefore, as given in the algorithms, thedesired compression forces for all of the dynamics associated with agiven suspension unit are added together to obtain one desiredcompression force for that unit, represented by block 252 in FIG. 7.This is repeated for each unit for both compression and rebound (block254), to obtain complete and optimum control in real time. The formulasfor these composite times appear as follows:

    F.sub.C =ΣF.sub.Ci =F.sub.C1 +F.sub.C2 . . . F.sub.C9

    F.sub.R =ΣF.sub.Ri =F.sub.R1 +F.sub.R2 . . . F.sub.R9

The above formulas apply to one suspension unit. For total control eachsuspension unit has inputs of a composite F_(C) and F_(R) for eachcontroller cycle time. Most intermediate computations are done once andshared among the suspension units as would be easily perceived from thepreceding discussion. Each controller update cycle time computes thenext setting for F_(C) and F_(R) using the tables in memory and summingin accordance with the above equations.

It is well to note that the apparent complexity is more apparent thanreal. For example, many computed parameters such as P.sub.Δ are doneonly once per cycle per suspension unit. Only their usage changes. Forexample, P.sub.Δ for roll control of the left front wheel is P'.sub.Δfor roll control of the right front wheel and P".sub.Δ for pitch controlof the left rear wheel, and so on. In addition, the tables stored forthe table look-up operations are also shared. The table given in theexample for roll control could apply to all four suspension units, thatis, only one table for roll control would be required in the entiresoftware.

When properly applied to the appropriate suspension units, these controlalgorithms will result in smoothly varying control forces that areessentially independent of what the wheels are doing. These forces willbe stabilizing and controlling the vehicle in a near optimum way. Whennecessary, such as in bottoming out control, forces will be applied tothe chassis but only as required and will smoothly and comfortably varyrates of change.

A preferred embodiment of control 22 will now be described withreference to FIG. 11. The components illustrated within the dottedoutlines may be repeated as necessary dependent upon the desired systemcontrol. This control system simultaneously controls all of thesuspension units associated with the different wheels of the vehicle andspecifically refers to the suspension unit shown in FIGS. 2 and 3. Thecontrol includes a computer 118 such as a microprocessor having suitableRAM and ROM memories coupled to the microprocessor for storingcomputation information and operational programs, respectively. Thecomputer has input ports 120 connected thereto for receiving signalsfrom various transducers within the suspension units. Referring to FIG.3, these include the piston position sensors or transducers 82 on eachsuspension unit and air pressure sensors 99 and 101 on some or all ofthese suspension units.

While hydraulic sensor 82 comprises a transducer, a signal source 122may be connected to the input of the transducer and the output of thetransducer is connected to detector 124. Analog to digital converters126 convert the analog signals from the transducers in the suspensionunits into digital form before they are input to computer 118 throughthe input ports. Using the operational programs stored in the ROM of thecomputer, the microprocessor continuously determines the optimumcompression and rebound damping forces as well as the optimum springrate. Commands are sent from the computer to control pump 96, airpressure inlet and outlet regulators 40 and 42 on some or all of thesuspension units and compression and rebound regulators 36 and 38 oneach suspension unit.

Output ports 128 provide the interface between computer 118 and thedevices which it controls. Digitally controlled switches 130 areutilized to turn air pump 96 on and off and to open and close the airpressure valves 40 and 42. Digital to analog converters 131, currentsources 132 and optional high voltage supply 134 are utilized togenerate the signals necessary to control hydraulic compression andrebound pressure regulators 36 and 38.

Variations of the system are illustrated in FIGS. 12 and 13. FIG. 12shows the simplest possible electrically controllable shock absorber.Shock absorber 200 is that of any conventional design. The variation isthat the first stage valving or "bleed orificing" includes orifice 406in a piston 401 which is set for very rapid pressure buildup or may beremoved from improved roll control and performance.

An example of this type of valving is provided in FIG. 12. The sectionalview of piston 401 shows a pair of orifices 402 and 403 extendingthrough piston 401 to provide passageways for hydraulic fluid to flowbetween compression and rebound chambers during reciprocation by thepiston. A spring loaded valve 404, at the lower opening of orifice 402,when a certain pressure is reached, operates to allow hydraulic fluid toflow through the orifice during compression of the shock absorber butremains closed during rebound. Conversely, a spring loaded valve 405, atthe lower opening of orifice 403, operates to allow fluid to flowthrough the orifice when a certain pressure is reached during rebound ofthe shock absorber but remains closed during compression. The diameterof these orifices may be selected to provide the appropriate valvecharacteristics. It is to be understood that other conventional highperformance valving could also be used in this variation of theinvention. For example, the bleed orifice 406 may be eliminated.

Although the valves in the piston and orifice 406 have been describedwith reference to FIG. 12, these same elements may be employed with thepiston 58 and rod 24 in the embodiment of FIG. 3 which includes springs68 and 70.

A solenoid pressure regulator valve 220 of the preferred embodiment isconnected to the compression chamber by means of conduit 230 and to therebound chamber by means of conduit 240. Control 210, which may beeither manual or automatic, can be made to set the initial first stageblow off pressure on compression to any level from very little pressurefor soft control to very high pressure for stiff control. This isaccomplished by allowing valve 220 to bypass the fluid flow around thefirst stage orificing within shock absorber 200 upon compression.

FIG. 13 illustrates a variation that is capable of much higherperformance. In FIG. 3, the fluid pressure in chamber 61 is obtained byfluid flow through passage 114 due to the bias pressure generated by theaction of spring 79 on spool 74. This flow is limited for soft ridecharacteristics. If chamber 61 is isolated from the fluid in the shockabsorber and connected to an external fluid pressure supply as shown inFIG. 13, then faster response may be obtained. Referring specifically toFIG. 13, shock absorber 300 is that shown in FIG. 3 but with spring 79removed and passage 114 blocked. Passage 88 in FIG. 3 is connected topassage 350 in FIG. 13. Passage 89 in FIG. 3 is connected to passage 355in FIG. 13. The operation of the system illustrated in FIG. 13 is asfollows.

The blow off pressure of spool 74 in FIG. 3 is still set by the pressureon chamber 61. However, the fluid pressure in chamber 61 is set by valve36 with the fluid flow into chamber 62 provided through passage 350 froma high pressure fluid accumulator 320 as shown in FIG. 13. The returnfluid flow from valve 36 in FIG. 3 goes to a fluid reservoir 330. Pump330 is then connected between accumulator 320 and reservoir 330 by meansof passages 340 and 345 to recharge accumulator 320.

It should be apparent that there are many variations of the shockabsorber structure and the control connections which may utilize thepressure regulator solenoid valve and amplifying valve in differentcombinations. In particular, the amplifying valve can have spring 80removed and spools 74 and 76 attached as one unit. The main blow offorifice 115 would normally be open. When pressure in chamber 61 isincreased due to valve 36, the larger area at spool 76 is attacheddirectly to spool 74 and the blow off flange causes the pressure inchamber 60 to reach a multiple of that in chamber 61 at all times formuch higher performance.

Another variation of valve 72 occurs when amplification is not required.In this case spring 78 is removed and spool 76 is rigidly attached tothe valve body such as at seat 117. The surface area of spool 74 facingchamber 61 can be made equal to the surface area of spool 74 facingchamber 60. In such case pressure settings in chamber 61 are equal tothat in chamber 60 for blowoff conditions at orifice 115.

There are a number of key points and factors which are important to keepin mind with respect to this invention and which have been referred toabove. A listing of these factors follows:

1. any number of parameters can be accommodated by the system, forexample, pumping down may be omitted, or others may be added.

2. The description is for a four-wheel vehicle, but the principles areapplicable to any number, even a multi-wheeled vehicle for off road ormilitary use.

3. Position of the main piston in the shock absorber represents theposition of the axle with respect to the chassis.

4. Position output signals are not necessarily required from everysuspension unit of a vehicle, but it is highly desirable that there byposition signals from each wheel of a four-wheel vehicle.

5. The desired responses programmed in FIG. 7 can be determined eitherfrom solution of equations or table look-up, with the latter generallybeing faster.

6. Spring rate output signals may be from any number of the suspensionunits, from zero to all the springs.

7. Similarly, the spring rate controls (SR_(I) and SR_(D)) can be anynumber, for example both front springs or both rear springs can becontrolled together, or all four can be controlled together.

8. Actual calculations performed can be simplified by using many resultsin common with others, but the principles of analysis can be consideredseparately for each parameter.

9. The control algorithms may be any type or form desired. Thoseprovided are by way of example and for purposes of completeness ofdescription.

10. This system applies to any suspension unit capable of having asignal output representing position and being controllable by inputsthat control compression and rebound damping.

11. The system provides the enumerated advantages at relatively low costand weight, improves aerodynamics with the height control function,adapts for wear automatically, utilizes conventional manufacturing, ishighly reliable, employs low (10%) tolerance components and provides aluxury ride simultaneously with high stability performance.

In summary, this control system provides a cost effective suspensionusing microprocessor technology to achieve fundamental suspensioncontrol of any vehicle while approaching the theoretical limit ofsuspension performance and providing near ideal ride characteristics.

In view of the above description and examples, it is likely thatmodifications and improvements which are within the scope of theaccompanying claims will occur to those skilled in the art.

What is claimed:
 1. A control system for one or more damping devicescomprising extensible shock absorber means for damping between twomasses in compression and rebound directions, sensor means forgenerating signals representative of the degree of the extension of theshock absorber means, and regulator means responsive to independentcompression control signal and rebound control signal for adjusting,respectively, the compression direction force and the rebound directionforce presented by the shock absorber means to the extension, thecontrol system comprising:means for receiving signals, representative ofthe degree of the extension, generated by the sensor means, processingmeans for processing the received signals to determine one or moreindependent parameters each representative of a distinct state of motionof the two masses, for using each of the parameters to determine, foreach of the shock absorber means, a desired independent response foreach of the distinct states of motion, and for processing the desiredindependent responses for each of the individual shock absorber means toform compression control signal and rebound control signal for each ofthe regulator means.
 2. A system according to claim 1 wherein theprocessing means is a digital processor adapted to sample the receivedsignals rapidly a plurality of times per second and for providing thecontrol signals rapidly a plurality of times per second.
 3. A system asdescribed in claim 1 wherein the processing means is adapted to permitaltering of the desired independent response that the processing meansdetermines for given parameters.
 4. A system as described in claim 1wherein the processing means comprises a table for use by the processingmeans for converting the parameters to the desired independentresponses.
 5. A control system for a plurality of damping devices, eachdamping device comprising extensible shock absorber means for dampingbetween sprung and unsprung masses in a vehicle, sensor means forgenerating signals representative of the degree of extension of theshock absorber means, and regulator means responsive to independentcompression control signal and rebound control signal for adjusting,respectively, the compression direction force and the rebound directionforce presented by the shock absorber means to the extension, thecontrol system comprising:means for receiving signals generated by eachof the sensor means representative of the degree of extension,processing means adapted to determine from the received signals aplurality of independent parameters each representative of a distinctstate of motion of the vehicle, for using the plurality of parameters todetermine, for each individual shock absorber means, a desiredindependent response for each of the distinct states of motion, and forprocessing the desired independent responses for each of the individualshock absorber means to form, for each of the regulator means,independent compression control signal and rebound control signal.
 6. Acontrol system according to claim 5 comprising means for providing theindependent compression control signal and rebound control signal toeach regulator means.
 7. A control system according to claim 5 whereinthe processing means comprises a digital microprocessor.
 8. A controlsystem according to claim 5 wherein one of the parameters is a functionof the amount of roll of the vehicle.
 9. A control system according toclaim 5 wherein at least one of the parameters is a function of theamount of pitch of the vehicle.
 10. A control system according to claim5 wherein at least one of the parameters is a function of the amount ofpump-down of at least one of the damping devices.
 11. A control systemaccording to claim 5 wherein at least one of the parameters is afunction of the amount of stored energy in a compression spring.
 12. Acontrol system according to claim 5 wherein at least one of theparameters is a function of the amount of natural frequency of theunsprung mass.
 13. A control system according to claim 5 wherein atleast one of the parameters is a function of the amount of naturalfrequency of the sprung mass.
 14. A control system according to claim 5wherein at least one of the parameters is a function of thesusceptibility of the sprung mass to bottom-out against the unsprungmass.
 15. A control system according to claim 5 wherein at least one ofthe parameters is a function of the susceptibility of the sprung mass totop-out against the unsprung mass.
 16. A control system according toclaim 5 wherein the processing means is adapted to permit selectivealtering of the desired independent response that the processing meanswill determine from the parameter representative of a distinct state ofmotion determined.
 17. A control system according to claim 5 wherein theprocessing means is adapted to determine the desired independentresponses from the parameters representative of a distinct state ofmotion by using a table cross-referencing the appropriate responses forall parameters.
 18. A control system for a vehicle according to claim 5wherein there is, corresponding to each damping device, controllable airspring means wherein the processing means is adapted to determine, fromthe signals generated by the extension sensor means, a plurality offurther parameters each representative of a further distinct state ofmotion of the vehicle, for using the plurality of further parameters todetermine, for each air spring means, a further desired independentresponse for each of the further distinct states of motion, and forprocessing the further desired independent responses for each of theindependent controllable air spring means for forming a control signalfor controlling spring rate in each controllable air spring means.
 19. Acontrol system according to claim 18 wherein there is at least onepressure sensor means for sensing the pressure in at least one of thecontrollable air spring means, and further comprising means forreceiving signals generated by the at least one pressure sensor means,the processor means further being adapted for using such received signalin determining at least one of the desired independent responses,thereby improving the same.
 20. A control system according to either ofclaims 5 or 18 wherein the processing means is adapted for combining theindependent responses together to form the control signals.
 21. A methodfor controlling one or more damping devices comprising extensible shockabsorber means for damping between two masses in compression and rebounddirections, sensor means for generating signals representative of thedegree of the extension of the shock absorber means, and regulator meansresponsive to independent compression control signal and rebound signalfor adjusting, respectively, the compression direction force and therebound direction force presented by the shock absorber means to theextension, the method comprising:receiving the signals, representativeof the degree of the extension, generated by the sensor means,processing the received signals to determine one or more independentparameters each representative of a distinct state of motion of the twomasses, determining a desired independent response from the independentparameters for each of the distinct states of motion, and forming acompression control signal and a rebound control signal for each of theregulator means from the determined desired independent response.
 22. Amethod for controlling a plurality of damping devices, each dampingdevice comprising extensible shock absorber means for damping betweensprung and unsprung masses in a vehicle, sensor means for generatingsignals representative of the degree of extension of the shock absorbermeans, and regulator means responsive to independent compression controlsignal and rebound control signal for adjusting, respectively, thecompression direction force and the rebound direction force of the shockabsorber means to the extension, the method comprising:receiving signalsgenerated by each of the sensor means representative of the degree ofextension, determining therefrom a plurality of independent parameterseach representative of a distinct state of motion of the vehicle, usingthe plurality of parameters to determine, for each individual shockabsorber means, a desired independent response for each of the distinctstates of motion, and processing the desired independent responses foreach of the individual shock absorber means to form, for each of theregulator means, independent compression control signal and reboundcontrol signal.
 23. A method according to claim 22 comprising the stepof providing the compression control signal and the rebound controlsignal to each of the shock absorber means.
 24. A method according toclaim 22 wherein the steps of determining and processing comprise thestep of programming a digital microprocessor.
 25. A method according toclaim 22 wherein at least one of the parameters is a function of theamount of roll of the vehicle.
 26. A method according to claim 22wherein at least one of the parameters is a function of the amount ofpitch of the vehicle.
 27. A method according to claim 22 wherein atleast one of the parameters is a function of the amount of pump-down ofat least one of the damping devices.
 28. A method according to claim 22wherein at least one of the parameters is a function of the amount ofstored energy in a compression spring.
 29. A method according to claim22 wherein at least one of the parameters is a function of the amount ofnatural frequency of the unsprung mass.
 30. A method according to claim22 wherein at least one of the parameters is a function of the amount ofnatural frequency of the sprung mass.
 31. A method according to claim 22wherein at least one of the parameters is a function of thesusceptibility of the sprung mass to bottom-out against the unsprungmass.
 32. A method according to claim 22 wherein at least one of theparameters is a function of the susceptibility of the sprung mass totop-out against the unsprung mass.
 33. A method according to claim 22wherein the processing means is adapted to permit selective altering ofthe desired independent response that the processing means willdetermine from the parameter representative of a distinct state ofmotion determined.
 34. A method according to claim 22 wherein theprocessing means is adapted to determine the desired independentresponses from the parameters representative of a distinct state ofmotion by using a table cross-referencing the appropriate responses forall parameters.
 35. A method according to claim 22 wherein there is,corresponding to each damping device, controllable air spring meanswherein processing includes determining, for each air spring means, afurther desired independent response for each of the further distinctstates of motion from the signals generated by the extension sensormeans, and processing the further desired independent responses for eachof the independent controllable air springs for forming a control signalfor controlling spring rate in each controllable air spring.
 36. Themethod of claim 35 further including sensing the pressure of at leastone of the controllable air spring means and generating signalscorresponding to the sensed pressure, the processing step furtherincluding determining the further desired independent response inresponse to the sensed pressure signals thereby improving the same. 37.A method according to either of claims 22 or 35 wherein the steps ofprocessing comprise the steps of combining the independent responsestogether to form the control signals.
 38. A system for controlling aplurality of damping devices comprising:a cylinder for receivinghydraulic fluid; a piston rod; a piston mounted on the piston rod whichis reciprocable within the cylinder and defines therein a compressionchamber and a rebound chamber on opposite sides of the piston; sensormeans for generating signals representative of the position of thepiston within the cylinder; pressure regulator means coupled to thecompression chamber and pressure regulator means coupled to the reboundchamber for independently adjusting the pressure of the hydraulic fluidin the respective chambers during reciprocation of the piston inresponse to predetermined signals applied thereto; and control meansreceiving the signals from the sensor means characterized for using thesignals to determine the appropriate signals to be applied to eachpressure regulator means for optimal damping.
 39. A system forcontrolling a plurality of damping devices as described in claim 38wherein the damping devices are each adapted to be connected between adifferent point on sprung and unsprung masses of a vehicle to damp therelative motion of the masses with respect to one another and thecontrol means is further operative for processing the signals receivedfrom all the sensor means for determining and applying signals to eachpressure regulator means for composite optimal damping of the vehicle.40. A controllable suspension system comprising: a plurality ofsuspension units, each unit comprising:spring means; sensor means incommunication with the spring means for generating signalsrepresentative of the spring rate of the spring means; regulator meanscoupled to the spring means for adjusting the spring rate of the springmeans in response to determined signals applied thereto; shock absorbermeans; sensor means in communication with the shock absorber means forgenerating signals representative of the degree of extension of theshock absorber means; regulator means coupled to the shock absorbermeans for independently adjusting the compression damping force of theshock absorber means and the rebound damping force of the shock absorbermeans in response to predetermined signals applied thereto; and controlmeans receiving the signals from the sensor means characterized forusing them to determine the signals to be applied to each suspensionunit regulator means for optimal performance of the suspension system.41. A system as described in claim 40 wherein the suspension units areeach adapted to be connected between different points on sprung andunsprung masses of a vehicle to cushion and damp the relative motion ofthe masses with respect to one another, and the control means is furtheroperative for processing the signals received from all the sensor meansfor determining and applying the signals to each regulator means forcomposite optimal ride and handling characteristics for the vehicle. 42.A damping system for control of long and short term variations ofdamping of wheel supporting a vehicle chassis, independently, incompression and rebound directions, the system comprising:a plurality ofseparate fluid controlled dampers, each of the dampers comprising amovable member adapted to be connected to one of such wheels, acompression fluid control means and a rebound fluid control means, eachdamper being responsive to control signals applied to the compressionfluid control means and to the rebound fluid control means for controlof the damping, relative to such chassis, of the corresponding member,and the wheel connected to such member in, respectively, compression andrebound directions; a plurality of sensors comprising an individualsensor for each damper for sensing displacement of a wheel, which isconnected to such damper, relative to such chassis; and control meanscoupled to all said sensors for applying control signals to thecompression and rebound fluid control means of all said dampers andcomprising means responsive to the sensors for varying the controlsignal applied to the compression fluid control means separate from thevarying of the control signal to the rebound fluid control means for anyof the dampers.
 43. A damping system according to claim 42 wherein thecontrol means comprises:means for controlling the control signals toeach of the inputs of each damper so as to cause each of the dampers topresent preselected damping to the corresponding member, and a connectedwheel, relative to such chassis for a time period; and means respondingto a momentary change, during the time period, in the seconddisplacement of at least one of the sensors for momentarily, during thetime period, varying the control signal applied to at least one of theinputs for at least one of the dampers separate from the control signalapplied to the other input of the same damper.
 44. A controlled damperfor damping the relative motion between two masses comprising:a cylinderconnected to one of the masses; a piston having a rod connected to theother of the masses, the piston received into the cylinder fortelescopic compression motion as the masses move together and reboundmotion as the masses move apart, the piston defining a separate fluidfilled compression chamber and rebound chamber within the cylinder;means for providing for restricted fluid communication between thechambers during compression and rebound motion; such restricted fluidcommunication damping such motion at a rate dependent upon a selecteddamping force; and means for separately controlling the restrictedcommunication during compression motions to establish a desiredcompression damping force and during rebound motion to establish adesired rebound damping force.
 45. A control system for one or moredamping devices comprising extensible shock absorber means for dampingbetween two masses in compression and rebound directions, sensor meansfor generating signals representative of the degree of extension of theshock absorber means, and regulator means responsive to at least onecontrol signal for adjusting at least one of the compression directionforce and the rebound direction force presented by the shock absorbermeans to the extension, the control system comprising:means forreceiving signals, representative of the degree of extension, generatedby the sensor means, processing means for processing the receivedsignals to determine one or more independent parameters eachrepresentative of a distinct state of motion of the two masses, forusing each of the parameters to determine, for each of the shockabsorber means, a desired independent response for each of the distinctstates of motion, and for processing the desired independent for each ofthe individual shock absorber means to form at least one control signalfor at least one of the regulator means.
 46. A method for controllingone or more damping devices comprising extensible shock absorber meansfor damping between two masses in compression and rebound directions,sensor means for generating signals representative of the degree ofextension of the shock absorber means, and regulator means responsive toat least one control signal for adjusting at least one of thecompression direction force and the rebound direction force presented bythe shock absorber means to the extension, the methodcomprising:receiving the signals, representative of the degree ofextension, generated by the sensor means, processing the receivedsignals to determine one or more independent parameters eachrepresentative of a distinct state of motion of the two masses,determining a desired independent response from the independentparameters for each of the distinct states of motion and forming atleast one control signal for at least one of the regulator means fromthe determined desired independent response.